Dam a ‘Significant Hazard’

COURT HOUSE – Middle Township Committee heard a presentation Aug. 19 on the state Department of Transportation (NJDOT) project to bring the Nummytown Mill Pond Dam on Route 47 in Rio Grande into compliance with New Jersey Dam Safety standards.
Greenman-Pedersen, Inc. (GPI), an engineering firm with an office in Ocean View, presented a series of options for the dam’s reconstruction.
With the assistance of former county engineer Dale Foster, a senior project manager for GPI, the company presented 12 alternatives for bringing the 1925 dam into compliance.
NJDOT documents describe the FY2016-2025 improvement at an estimated $1.8 million. 
Those documents list the source of funding as the National Highway Performance Program, federal funds aimed at improving the condition and support of the national highway system.
The Class 2, almost 100-year-old dam is cited as a “significant hazard.”
The dam, and the bridge that is integral to it, sits north of the Wildwood Water pumping station on Route 47. The concrete slab bridge is non-conforming.
The 32-foot-wide bridge connects to the 40-foot-wide Route 47 at both ends of its 10-foot span. One option would be a replacement for the bridge that would be 26 feet long and the proper width for the roadway.
The presentation stated the dam has insufficient spillway capacity, which could result in overflow during flooding events. The overflow then becomes potentially damaging to the slope opposite the pond area, aiding in the crumbling of spillway channel walls.
Foster said the analysis on the hazard is based on the flooding that would occur with a 100-year storm.
The alternatives presented ranged from a minimalist option of hardening the downstream slope, which does little to relieve other areas of non-compliance, to bridge replacement accompanying other work on the spillway channel.
When asked by Mayor Timothy Donohue if an option that included replacement of the bridge was likely, Foster did not commit to an answer. He said the bridge has had minimal work since its installation in 1925.
The difficulties involved in bridge replacement focus on traffic interruption on one of the municipality’s major thoroughfares.
Foster described two possible alternatives for replacing the bridge.
The first involved closing the roadway completely during one off-season and redirecting all traffic around detours that would eventually put it back on Route 47.
This option would produce the most temporary pain but would also complete the work faster.
The other option is to work one side of the bridge at a time taking out northbound and then southbound lanes in two successive off-seasons. One-way traffic in the bridge area would be controlled by lights, Foster said.
A decision is pending state review of the most viable alternatives for bringing the dam into compliance.
Foster outlined a process in which the conceptual options would be reviewed, followed by a permitting process involving environmental issues with federal and state officials.
He also mentioned the need to remove trees in the area of dam construction and the follow-on requirement for a reforestation plan to mitigate the impact of the tree removal.
Foster estimated that the project is probably a three- to four-year effort with the first two years of pre-construction endeavors taken up with design work and permitting processes. Construction time would vary with the alternative selected.
Foster said a mandatory public information session may be held as early as September, followed by the selection of a preliminary preferred alternative later in the fall.
To contact Vince Conti, email vconti@cmcherald.com.